lark-parser #618

lark_tree_to_json.py

"""
lark_tree_to_json.py

How can I convert the output of lark().parse() into JSON #618
  https://github.com/lark-parser/lark/issues/618

Lark parser, LALR & Earley, Python
  https://github.com/lark-parser/lark
  https://lark-parser.readthedocs.io/en/latest/
  https://pypi.org/project/lark-parser/
"""

def tree_to_json_str(item):
    output = []
    tree_to_json(tree, output.append)  # will build output in memory
    return ''.join(output)

def tree_to_json(item, write=None):
    """ Writes a Lark tree as a JSON dictionary. """
    if write is None: write = sys.stdout.write
    _tree_to_json(item, write, 0)

def _tree_to_json(item, write, level):
    indent = '  ' * level
    level += 1
    if isinstance(item, lark.Tree):
        write(f'{indent}{{ "type": "{item.data}", "children": [\n')
        sep = ''
        for child in item.children:
            write(indent)
            write(sep)
            _tree_to_json(child, write, level)
            sep = ',\n'
        write(f'{indent}] }}\n')
    elif isinstance(item, lark.Token):
        # reminder: Lark Tokens are directly strings
        # token attrs include: line, end_line, column, end_column, pos_in_stream, end_pos
        write(f'{indent}{{ "type": "{item.type}", "text": "{item}", "line": {item.line}, "col": {item.column} }}\n')
    else:
        assert False, item  # fall-through

# get a grammar
import sys
sys.path.insert(0, 'examples')
import calc
grammar = calc.calc_grammar

# get some code to parse
code = '3 + 5 * 12'

# parse with lark
import lark
parser = lark.Lark(grammar, parser='lalr')
tree = parser.parse(code)
print(tree.pretty())

# print with tree_to_json
tree_to_json(tree)  # will print to stdout

# build JSON string with tree_to_json_str
json_str = tree_to_json_str(tree)

# test that above JSON string is valid
import json
parsed_json = json.loads(json_str)
print(parsed_json)
assert isinstance(parsed_json, dict)
assert parsed_json['type'] == 'add'
assert len(parsed_json['children']) == 2